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The role of Fe and cation order in the crystal chemistry of surinamite, (Mg,Fe (super 2+) ) (sub 3) (Al,Fe (super 3+) ) (sub 3) O[AIBeSi (sub 3) O (sub 15) ]; a crystal structure, Moessbauer spectroscopic, and optical spectroscopic study

Jacques Barbier, Edward S. Grew, Elke Halenius, Ulf Halenius and Martin G. Yates
The role of Fe and cation order in the crystal chemistry of surinamite, (Mg,Fe (super 2+) ) (sub 3) (Al,Fe (super 3+) ) (sub 3) O[AIBeSi (sub 3) O (sub 15) ]; a crystal structure, Moessbauer spectroscopic, and optical spectroscopic study
American Mineralogist (April 2002) 87 (4): 501-513

Abstract

The crystal structure of surinamite from "Christmas Point," Enderby Land, Antarctica, has been newly refined by single-crystal X-ray diffraction: (super VI) (Mg (sub 2.26) Fe (super 2+) (sub 0.74) Fe (super 3+) (sub 0.39) Al (sub 2.61) )O (super IV) (Al (sub 1.00) Be (sub 1.00) Si (sub 3.00) )O (sub 15) (simplified formula), space group P2/n, a = 9.915(2), b = 11.368(2), c = 9.617(2), b = 109.30(2) degrees , Z = 4, wR(F (super 2) ) = 0.074 for 4876 independent reflections. The refined site occupancies agree well with the chemical composition determined by electron microprobe analysis and with the Fe (super 3+) /Fe (super 2+) ratio estimated from stoichiometry. The surinamite structure is characterized by an ordered Al/Be/Si distribution on the tetrahedral sites and by charge ordering with extensive Mg (super 2+) -Fe (super 2+) and Al (super 3+) -Fe (super 3+) exchange on the octahedral sites. This cation ordering is distinct from that observed in related phases of the sapphirine series and aenigmatite groups, and the difference is linked to the unique structural topology of the tetrahedral chains in surinamite. Optical and Mossbauer spectra of surinamite have been fully interpreted in terms of an octahedral distribution of Fe (super 2+) and Fe (super 3+) cations that agrees very well with the X-ray site populations. Both the X-ray and Mossbauer data establish the absence of significant tetrahedral Fe and the non-uniform distribution of octahedral Fe. Intense and strongly polarized absorption bands caused by IVCT-processes in clusters of Fe (super 3+) and Fe (super 2+) iron in edge-sharing octahedral sites produce the unusual color and pleochroism observed in surinamite.


ISSN: 0003-004X
EISSN: 1945-3027
Coden: AMMIAY
Serial Title: American Mineralogist
Serial Volume: 87
Serial Issue: 4
Title: The role of Fe and cation order in the crystal chemistry of surinamite, (Mg,Fe (super 2+) ) (sub 3) (Al,Fe (super 3+) ) (sub 3) O[AIBeSi (sub 3) O (sub 15) ]; a crystal structure, Moessbauer spectroscopic, and optical spectroscopic study
Affiliation: McMaster University, Department of Chemistry, Hamilton, ON, Canada
Pages: 501-513
Published: 200204
Text Language: English
Publisher: Mineralogical Society of America, Washington, DC, United States
References: 50
Accession Number: 2002-047418
Categories: Mineralogy of silicates
Document Type: Serial
Bibliographic Level: Analytic
Annotation: NSF Grant OPP-0087235
Illustration Description: illus. incl. 9 tables
Secondary Affiliation: University of Maine, USA, United StatesSGAB Analytica, SWE, SwedenSwedish Museum of Natural History, SWE, Sweden
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute.
Update Code: 200216
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